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Is a portion of the aponeurotic sheath which envelops the whole of the upper limb. It arises from the brachial aponeurosis, from a fibrous expansion of the tendon of the biceps muscle, from the epicondyle, epitrochlea, and, behind, from the tendon of the triceps brachialis. Within, it is inserted into the cubitus, etc.; and, below, is confounded with the two annular ligaments of the carpus. It is covered by the skin, by veins, lymphatics, and by filaments of superficial nerves; it covers the muscles of the fore-arm, adheres to them, and sends between them several fibrous septa, which serve them for points of insertion.